Plasma Pyridoxal Phosphate Concentrations Research Articles

Effect of a swim training on homocysteine and cysteine levels in rats

The purpose of this study was to investigate the effects of a 8-week of swim training on total plasma homocysteine and cysteine levels in 16 male Sprague-Dawley rats aged 17 weeks. We also evaluated the activity of hepatic cystathionine beta-synthase (CBS), an enzyme involved in the metabolism of Hcy, the concentration of plasma glutathione, taurine, and a fraction of vitamin B6: the pyridoxal 5-phosphate (PLP). After one week of acclimatization, rats were randomly divided into two groups: 8 non-trained (NTR) and 8 trained rats (TR). Following the training period, body weight gain was lower in TR than in NTR. Plasma homocysteine did not differ among groups while significantly lower plasma cysteine and taurine levels were found in TR (157.83 +/- 8.6 micromol/L; 133.01 +/- 9.32 micromol/L; P < 0.05) compared with data of NTR (176.19 +/- 4.9 micromol/L; 162.57 +/- 8.16 micromol/L; P < 0.05). No significant changes in hepatic CBS activity were observed in TR compared with NTR. Moreover, values for plasma glutathione and PLP concentrations were not affected by training.These results indicate that training reduces plasma cysteine and taurine levels whereas it does not modify other studied parameters. Thus, physical training may regulate cysteine metabolism.

B-6 vitamers and 4-pyridoxic acid in the plasma, erythrocytes, and urine of postmenopausal women

Although many studies have reported reduced vitamin B-6 status with aging, little information is available about the specific effects of menopause. We aimed to examine vitamin B-6 metabolism in premenopausal and early postmenopausal women. We examined dietary intake and vitamin B-6 metabolites in the plasma, erythrocytes, and urine of 30 premenopausal women (x +/- SD age: 41.9 +/- 4.8 y) and 30 women (aged 54.0 +/- 3.8 y) who were 4.0 +/- 1.4 y past menopause. Vitamin B-6 intake in the postmenopausal group (1.97 +/- 0.40 mg/d) was significantly greater than that in the premenopausal group (1.63 +/- 0.50 mg/d). Plasma pyridoxal phosphate (PLP) and pyridoxal concentrations and erythrocyte PLP, pyridoxal, and pyridoxamine phosphate concentrations were in the normal range in both groups and did not differ significantly between the 2 groups. Plasma and erythrocyte 4-pyridoxic acid (4-PA) concentrations were significantly higher in the postmenopausal group than in the premenopausal group, which may have been due at least partly to the slightly higher vitamin B-6 intake of the former group. Erythrocyte 4-PA was correlated (r = -0.37, P < 0.01) with serum estradiol in both groups. Urinary 4-PA did not differ significantly between the 2 groups. The serum phosphate concentration was higher in the postmenopausal group than in the premenopausal group, and it was correlated (r = 0.40, P < 0.01) with plasma PLP. Inhibition of alkaline phosphatase by the increased phosphate may help to increase plasma PLP. Menopause may not necessarily be associated with a decrease in vitamin B-6 status.

Evaluation of Vitamin B6 Status and RDA in Young Koreans

Aims and Methods: The vitamin B₆ status of 294 healthy young Koreans (149 men, 145 women), aged 17–25 years, was estimated to establish the Korean Recommended Dietary Allowance (RDA) for vitamin B₆. The dietary vitamin B₆ intake was estimated based on a three-day recall method. Results: The average daily vitamin B₆ intake of the subjects was 1.504 ± 0.825 mg/day (1.567 ± 0.968 mg/day for men and 1.439 ± 0.644 mg/day for women). The average ratio of vitamin B₆ intake to daily protein intake was 0.019 ± 0.001 mg/g (0.015 ± 0.001 mg/g for men and 0.023 ± 0.001 mg/g for women). Foods from animal and plant sources provided 35.68 ± 16.16 and 64.18 ± 16.29% of total vitamin B₆. Plasma pyridoxal 5′-phosphate (PLP) concentration of the subjects was 29.26 ± 16.84 nmol/l (30.52 ± 20.18 nmol/l for men and 28.21 ± 13.28 nmol/l for women). The vitamin B₆ intake of the subjects whose PLP concentration was >30 nmol/l was 0.019 ± 0.001 mg vitamin B₆/g protein intake (0.017 ± 0.001 and 0.023 ± 0.001 mg vitamin B₆/g protein intake for men and women, respectively). The intake of vitamin B₆ was significantly (p < 0.01–p < 0.001) positively correlated with the intake of all other nutrients. However, no significant correlation was found between PLP concentration and all nutrients examined. Conclusion: Our suggested adequate Korean RDA for vitamin B₆ in young Koreans is 1.6 mg/day or 0.02 mg/g of protein intake in men and 1.5 mg/day or 0.02 mg/g of protein intake in women.

Low plasma vitamin B-6 concentrations and modulation of coronary artery disease risk

Low concentrations of pyridoxal-5'-phosphate (PLP), the active metabolite of vitamin B-6, are associated with high C-reactive protein (CRP) concentrations. Both low PLP and elevated inflammatory markers, such as high-sensitivity CRP (hs-CRP) and fibrinogen, are related to higher risk of coronary artery disease (CAD). The objectives were to evaluate the relation between PLP and acute-phase reactants in affecting CAD risk and to estimate the risk of CAD related to low plasma PLP, either alone or in combination with high concentrations of acute-phase reactants and other classic risk factors for CAD. A case-control study was conducted with 742 participants: 475 with severe multivessel CAD and 267 free from coronary atherosclerosis (CAD-free). We measured plasma PLP, fibrinogen, hs-CRP, and serum lipid concentrations and all major biochemical CAD risk factors, including total homocysteine. A significant, inverse, graded relation was observed between PLP and both hs-CRP and fibrinogen (P < 0.001). The prevalence of PLP concentrations in the lower half of the population (<50th percentile: 36.3 nmol/L) was significantly higher among CAD patients than among CAD-free subjects (P < 0.001). The odds ratio for CAD risk related to low PLP concentrations after adjustments for the major classic CAD risk factors, including hs-CRP and fibrinogen, was 1.89 (95% CI: 1.18, 3.03; P = 0.008). The CAD risk as a result of low PLP was additive when considered in combination with elevated hs-CRP concentrations or with an increased ratio of LDL to HDL. Low plasma PLP concentrations are inversely related to major markers of inflammation and independently associated with increased CAD risk.

The relationship between plasma and red cell concentrations of vitamins thiamine diphosphate, flavin adenine dinucleotide and pyridoxal 5-phosphate following elective knee arthroplasty

Background & aims: Water soluble vitamins B1, B2 and B6 are essential precursors for a wide variety of coenzymes involved in intermediary metabolism and their status is usually assessed from blood samples. The aim of the study was to examine the relationship between plasma and intra-cellular B-vitamins following the systemic inflammatory response of surgery. Methods: Patients ( n=10) who underwent an elective knee arthroplasty, had venous blood samples withdrawn pre-operatively and at 12, 24, 48, 72 and 168 h after the start of surgery for the analysis of circulating concentrations of C-reactive protein and albumin and also plasma and/ or red cell thiamine diphosphate (TDP), flavin adenine dinucleotide (FAD), pyridoxal 5-phosphate (PLP) as indicators of vitamins B1, B2, and B6 status respectively. Results: Pre-operative, baseline vitamin assessments were all within population reference ranges. Over the study period of 0–168 h there was a significant increase in circulating C-reactive protein concentrations (peak 48 h, P<0.001) and a significant fall in albumin concentrations (trough 48 h, P<0.001). Plasma FAD and PLP concentrations fell transiently ( P<0.001) by approximately 40% reaching their nadir at approximately 48 h. Conclusions: The results of the present study indicate that plasma concentrations of FAD and PLP are transiently reduced following an inflammatory insult and therefore unlikely to be a reliable measure of status in the presence of a systemic inflammatory response. It may be that during such a response red cell concentrations provide a more reliable measure.

Pyridoxal phosphate decreases in plasma but not erythrocytes during systemic inflammatory response.

Vitamin B6 (active 3 hydroxy-2-methylpyridine derivatives) is an essential precursor of pyridoxal (PL) and pyridoxamine phosphate coenzymes of a wide variety of enzymes of intermediary metabolism (1). In plasma, pyridoxal 5′-phosphate (PLP) is the major form, whereas PLP and pyridoxamine 5′-phosphate (PMP) predominate in the cell. The most widely used method to detect vitamin B6 deficiency is the erythrocyte aspartate aminotransferase activation assay (2)(3)(4)(5). As this test is a functional rather than a direct measurement of PLP status, it may be affected by factors other than PLP deficiency (2)(3). The plasma PLP concentration is considered one of the better indicators of vitamin B6 status (1)(6)(7)(8)(9) and is reported to be well correlated with tissue PLP concentrations (8). However, vitamin concentrations in blood cells tend to be a better marker of cellular stores (10). We describe a simple, robust, reversed-phase HPLC method with precolumn derivatization using semicarbazide (11)(12)(13) that is suitable for the simultaneous measurement of PLP, 4-pyridoxic acid (PA), and PL in plasma and red cells and application of the assay in healthy individuals, patients with chronic disease, and critically ill patients requiring intensive care. Venous blood samples (EDTA) and packed red cells for population reference values were obtained from apparently healthy individuals (laboratory staff and those attending a cardiovascular risk clinic). Samples were obtained from a group of chronically ill medical and surgical patients with the potential for vitamin deficiencies (60% with short bowel syndrome and 35% with either chronic liver or renal disease) and from a critically ill group of medical and surgical patients admitted to the intensive care unit (30% with pancreatitis, 30% with trauma, 30% with organ failure). The study was approved by …

Determination of Vitamin B-6 Estimated Average Requirement and Recommended Dietary Allowance for Children Aged 7–12 Years Using Vitamin B-6 Intake, Nutritional Status and Anthropometry

The Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) of vitamin B-6 for children were recently estimated by extrapolating from adult values because of limited available information. To determine vitamin B-6 requirements and provide recommendations for intakes, vitamin B-6 intake, nutritional status and anthropometry of 168 healthy children (79 boys and 89 girls) were studied in Tainan, Taiwan. Direct and indirect vitamin B-6 status indicators were measured in plasma, erythrocytes and urine. Anthropometric data of children in this study were similar to those of the first Nutrition and Health Survey in Taiwan (NAHSIT) conducted in 1993-1996. The plasma pyridoxal phosphate (PLP) concentration of each child was >/=30 nmol/L, indicating an adequate vitamin B-6 status. Daily dietary vitamin B-6 intakes of boys and girls were 0.80 +/- 0.16 and 0.74 +/- 0.16 mg/d, respectively. Daily dietary vitamin B-6 intakes of children who had adequate urinary 4-pyridoxic acid (4-PA) (>3.0 micro mol/L), erythrocyte alanine aminotransferase activity coefficient (EALT-AC) (<1.25) and aspartate aminotransferase activity coefficient (EAST-AC) (<1.8) were not different from those of children who had adequate plasma PLP, although the percentages of adequacy for urinary 4-PA, EALT-AC and EAST-AC ranged from 20 to 91%. Vitamin B-6 status indicators were strongly correlated with vitamin B-6 intake. Adequate values of PLP, EALT-AC, EAST-AC and urinary 4-PA were used to determine the EAR according to Dietary Reference Intake (DRI) committee methodology. We determined the vitamin B-6 EAR (RDA) for boys and girls aged 7-12 y to be 0.84 (1.01) and 0.75 (0.89) mg/d, respectively.

Vitamin B6 intakes and status of mechanically ventilated critically ill patients in Taiwan.

To assess vitamin B6 intake and status of critically ill patients. The relationship between vitamin B6 status indicators and the severity of illness and outcome in these patients was also examined. Prospective clinical study. The study was performed at the Taichung Veteran General Hospital, in the central part of Taiwan. Ninety-four patients in the intensive care unit (ICU) entered the study and 46 patients successfully completed this study. No intervention. Vitamin B6 intake was recorded for 14 days. Vitamin B6 status was assessed by direct measures (plasma pyridoxal 5'-phosphate (PLP), pyridoxal (PL), and urinary 4-pyridoxic acid (4-PA)) and indirect measures (erythrocyte alanine (EALT-AC) and aspartate (EAST-AC) aminotransaminase activity coefficient). The severity of illness (APACHE II score), the length of ventilation dependency, and the length of ICU and hospital stay were recorded. Patients had an adequate mean vitamin B6 intake (16.26+/-19.39 mg) during the 14 day study. Mean vitamin B6 intake was significantly higher on day 14 than on day 1 (P<0.001). However, plasma PLP and PL concentrations significantly decreased at the 14th day after admission (P<0.05). Erythrocyte alanine aminotransaminase activity coefficient and EAST-AC did not change significantly. Urinary 4-PA significantly increased at the 14th day (P<0.001). No significant relationships were found between APACHE II scores and clinical outcomes (the length of ICU and hospital stay, the length of ventilation dependency) of patients, vitamin B6 intake or status indicators. Critically ill patients received nutritional support in the ICU, and had sufficient mean vitamin B6 intake and adequate vitamin B6 status. Therefore, the severity of illness and the results should not be affected by vitamin B6 status. However, we have noted that plasma PLP and PL concentrations significantly decreased while vitamin B6 intake significantly increased on day 14. Critical clinical conditions and complex metabolism in the critically ill may account for the reduction of plasma PLP and PL. Since vitamin B6 deficiency causes profound effects on immune system function, dietary or supplemented vitamin B6 intake is suggested for hospitalized patients.

Vitamin B6 status of breast-fed infants in relation to pyridoxine HCl supplementation of mothers.

The vitamin B6 nutritue of breast-fed infants was evaluated by vitamin B6 intake, plasma pyridoxal 5'-phosphate (PLP) concentration, and growth patterns during the infants' first 6 mo of age. Vitamin B6 intakes of 47 healthy, term infants were significantly correlated with four levels of maternal vitamin B6 supplements: 2.5, 4.0, 7.5, or 10.0 mg pyridoxine (PN) HCl/d and met the B6 Adequate Intake (AI, 1998) of 0.1 mg/d for infants 0 to 6 mo. Only infants whose mothers received 10.0 mg PN x HCl/d exceeded or met the Recommended Dietary Allowances (RDA, 1989) of 0.3 mg vitamin B6/d from 4 to 6 mo of age. Plasma PLP concentrations of infants, measured at 1, 4, and 6 mo of age paralleled their mother's vitamin B6 intake. Most infants showed normal growth. The findings indicated that a maternal PN x HCl supplement of 2.5 mg/d provided an adequate amount of vitamin B6 in breast milk (0.15 mg/d) for the vitamin B6 status parameters and the growth of breast-fed infants.

Vitamin B6 intakes and status assessment of elderly men and women in Taiwan.

Studies have indicated that vitamin B6 status decreases with age. However, little is known about vitamin B6 status of elderly people in Taiwan. The purpose of this study was to assess vitamin B6 status of elderly Taiwanese and to examine the effect of protein on various indices of vitamin B6 status in the elderly. Thirty-nine men (mean age = 69.9 +/- 4.2 years) and 55 women (mean age = 69.5 +/- 3.9 years) completed a 24-h diet recall. The mean total vitamin B6 intake (men: 1.7 +/- 0.9 g/day; women: 1.6 +/- 1.2 g/day) was higher than the 1998 US Dietary Reference Intakes (DRI) and the current Taiwan Recommended Daily Nutrient Allowance (RDNA). Dietary energy and protein intakes were not related to any vitamin B6 status parameters in any sex groups and the pooled group. Vitamin B6 intake correlated only with erythrocyte aspartate transaminase activity coefficient (EAST-AC) in the pooled (r = -0.214, p < 0.05) group. There were no significant differences in plasma pyridoxal 5'-phosphate (PLP), erythrocyte alanine transaminase activity coefficient (EALT-AC), and EAST-AC between sex groups. Although elderly subjects had adequate mean plasma PLP concentrations, 59% of men and 55% of women had plasma PLP concentrations lower than a cutoff of 20 nmol/L. The mean EALT-AC was < 1.25 in two groups with adequate vitamin B6 status. However, 23% of men and 18% of women had EALT-AC values > 1.25. The mean EAST-AC value of subjects was higher than the suggested value (< 1.8) for inadequate vitamin B6 status. The incidence of biochemical vitamin B6 deficiency in our elderly is probably more relevant from other causes than from dietary intake of protein and vitamin B6.

Assessment of Vitamin B-6 Status in Young Women Consuming a Controlled Diet Containing Four Levels of Vitamin B-6 Provides an Estimated Average Requirement and Recommended Dietary Allowance

The Recommended Dietary Allowance (RDA) of vitamin B-6 for young women was recently reduced from 1.6 to 1.3 mg/d based on an adequate plasma pyridoxal phosphate (PLP) concentration of 20 nmol/L. To assess vitamin B-6 requirements and suggest recommendations for intake, seven healthy young women consumed a controlled diet providing 1.2 g protein/kg body weight for a 7-d adjustment period (1.0 mg vitamin B-6/d) and three successive 14-d experimental periods (1.5, 2.1 and 2.7 mg/d, respectively). Direct and indirect vitamin B-6 status indicators were measured in plasma, erythrocytes and urine. Indicators most strongly correlated with vitamin B-6 intake [i.e., plasma and erythrocyte PLP, urinary 4-pyridoxic acid (4-PA) and total vitamin B-6] were regressed on vitamin B-6 intake and the dietary vitamin B-6 to protein ratio. Inverse prediction using adequate and baseline values estimated vitamin B-6 requirement. Adequate values were determined for plasma PLP and urinary 4-PA from baseline values of 60 previous subjects, using the statistical method suggested by Sauberlich. The current study suggests a vitamin B-6 Estimated Average Requirement (EAR) for young women of 1.1 mg/d or 0.016 mg/g protein, and a RDA of 1.5 mg/d or 0.020 mg/g protein. When results from this study are combined with data from four other recent studies, the combined data predict an EAR of 1.2 mg/d or 0.015 mg/g protein, and a RDA of 1.7 mg/d or 0.018 mg/g protein. This study suggests that the current vitamin B-6 RDA may not be adequate.

Fluctuations in Dietary Methionine Intake Do Not Alter Plasma Homocysteine Concentration in Healthy Men

A moderate elevation in plasma total homocysteine (tHcy) has been established as an independent risk factor for vascular disease. An important exogenous source of homocysteine is methionine found in foods rich in animal protein. We investigated the response of tHcy to fluctuations in methionine intake in a cross-over intervention trial (two arms). Healthy men (n = 52; 19-29 y) were screened for habitual methionine intake using a food-frequency questionnaire. Subjects in the top quartile for methionine intake (n = 13), with a baseline fasting tHcy of 7.01 +/- 1.84 micromol/L (mean +/- SD), were randomly assigned to receive either a low-methionine intervention diet for 1 wk followed by a control diet for 1 wk or vice-versa. Simultaneously, those in the bottom quartile for methionine intake (n = 11), with a fasting plasma tHcy of 9.79 +/- 7. 20 micromol/L (mean +/- SD), received either a high methionine intervention diet for 1 wk followed by a control diet or vice-versa. All subjects had serum folate, red-cell folate, serum vitamin B-12 and plasma pyridoxal phosphate (PLP) concentrations within normal ranges. During the intervention, subjects in the top quartile for methionine intake reduced their daily methionine intake 79%, from 1969 +/- 639 to 407 +/- 83 mg/d (P: </= 0.001), and those in the bottom quartile almost doubled their methionine intake, from 1155 +/- 401 to 2112 +/- 379 mg/d (P: </= 0.001). Despite these changes in methionine intake, no corresponding changes in plasma tHcy were observed. These results suggest that in the absence of an obvious deficiency of relevant B-vitamins, fasting plasma tHcy is unaffected by intermediate-term fluctuations (up to 100% of usual intake) in dietary methionine.

Plasma B-6 vitamer changes following a 50-km ultra-marathon.

The purpose of this study was to measure plasma B-6 vitamers, and other factors which may affect the plasma concentrations of these vitamers under extreme physical conditions. Blood samples were drawn from 8 men and 3 women (43.7 +/- 8.6 years) 30 min prior to the start of a 50-km ultramarathon race (pre), and at 5 (PST) and 60 (PST60) min post race. HPLC was used to measure plasma pyridoxal 5O-phosphate (PLP), pyridoxal (PL), pyridoxine (PN), and 4-pyridoxic acid (4-PA). Plasma glucose, albumin, lactate, and alkaline phosphatase activity, as well as hematocrit, and hemoglobin levels were measured. Food and liquid intake was assessed during the run. There was a significant (p <.001) decrease in the plasma PLP concentration between pre and PST, with a mean decrease of 12.9 +/- 8.8 nmol/L (31% decrease). At PST60, there was a further decrease in plasma PLP concentration bringing the total decrease to 17.9 nmol/L (44%). The plasma TB6 concentration also decreased after the run, but the mean decrease was only 13.5 nmol/L (pre to PST60). PL increased 25% after the run, and did not change further at PST60. The mean plasma 4-PA concentration increased 21% post run and decreased to just below the pre-run value 1 hr post race. The plasma PLP decrease measured in the current study is not consistent with what has previously been reported during shorter length endurance studies.

Vitamin B-6 Inadequacy Is Prevalent in Rural and Urban Indonesian Children

The vitamin B-6 status of Indonesian children was evaluated by determining their dietary vitamin B-6 intakes, erythrocyte alanine aminotransferase activity coefficients and plasma pyridoxal phosphate (PLP) concentrations. Thirty-eight third-grade elementary school children (ages = 8-9 y) in rural and 39 in urban areas of Bogor, West Java, Indonesia, voluntarily served as subjects. The subjects included 39 male and 38 female students. The mean vitamin B-6 intake of the subjects was 0.57 mg/d. Fifty-five percentage of the children reported consuming <0.5 mg/d of vitamin B-6 (the 1998 Estimated Average Requirement for those 4-8 y). Erythrocyte alanine aminotransferase activity coefficients >/= 1.25 were observed in 30%, and plasma PLP concentrations </= 30 nmol/L were observed in 25%; these values are considered indicative of vitamin B-6 inadequacy. Similar percentages of male and female subjects had inadequate vitamin B-6 status. Significantly more (P < 0.05) rural children than urban had inadequate vitamin B-6 status as assessed by the three indices. Vitamin B-6 inadequacy was found to be prevalent among these Indonesian children, especially those living in rural areas.

High performance liquid chromatography method for the determination of pyridoxal-5-phosphate in human plasma: how appropriate are cut-off values for vitamin B6 deficiency?

Application of a HPLC (high performance liquid chromatography) method, using cyanide derivatisation, to the determination of plasma pyridoxal-5-phosphate (PLP) concentrations as an indicator of vitamin B6 adequacy. The study was performed at the Institute of Food Research, Norwich, UK. Blood samples were taken at the Institute, at Health Centres, or in the volunteer's home. 51 adolescent, 131 adult, 68 non-institutionalized elderly and 44 aged (>73 y) volunteers were recruited from local authority schools, local Health Centres and General Practitioners. The mean PLP recovery was 92.8%. The intra- and inter-assay coefficients of variation were 2.8% and 5.2% respectively. Mean PLP concentrations for males and females, respectively, were: adolescents (13-14 y), 36.4 and 43.5 nM; adults (20-64 y), 39.2 and 40.0 nM; elderly (68-73 y), 34.8 and 35.3 nM; aged (>73 y), 57.8 and 49.0 nM. Percentages of subjects with PLP concentrations <34.4 nM were over 26% in all population groups. Mean vitamin B6 intakes (microg/g protein intake), as assessed by weighed dietary records, were all above reference nutrient intakes (15 microg/g protein). An HPLC method, using cyanide derivitisation, has been applied to the determination of plasma PLP. Comparisons of results for local population groups with current cut-off values for plasma PLP, show large numbers of volunteers at risk of vitamin B6 deficiency although this is not reflected by vitamin B6 intakes calculated from food tables. The 34.4 nM cut-off value for value for plasma PLP, indicating deficiency, is questioned.

Plasma pyridoxal phosphate and pyridoxic acid and their relationship to plasma homocysteine in a representative sample of British men and women aged 65 years and over

Concentrations of pyridoxal phosphate and pyridoxic acid were measured in fasting plasma samples from British men and women aged 65 years and over, participating in a National Diet and Nutrition Survey during 1994-5, selected to be representative of the population of mainland Britain. In this population, the concentration of pyridoxal phosphate declined, whereas pyridoxic acid rose, with increasing age and frailty; however, both status indicators were strongly and directly (with a positive coefficient) correlated with estimates of vitamin B6 intake. This was little affected by the inclusion of food energy and protein intakes in the model. Forty-eight percent of the participants living in the community and 75% of those living in institutions had plasma pyridoxal phosphate concentrations below a range considered normal from other studies. In a univariate regression model, plasma pyridoxal phosphate concentrations were inversely correlated with plasma homocysteine concentrations, consistent with the hypothesis that vitamin B6 status may influence plasma homocysteine levels, and hence vascular disease risk. However, this relationship was partly attenuated in a multiple regression model including age, sex, domicile and biochemical status indices, including those of folate and vitamin B12. There was evidence that plasma pyridoxal phosphate was sensitive to metabolic conditions associated with inflammation and the acute-phase reaction, and that plasma pyridoxic acid was sensitive to renal function. Thus, neither index is an ideal predictor of vitamin B6 status in older people, unless these confounding factors are allowed for. Since poor vitamin B6 status may have health implications, e.g. for immune function, cognition, and for essential intermediary metabolic pathways in older people, it needs to be investigated as a possible public health problem.

Adequacy of maternal pyridoxine supplementation during pregnancy in relation to the vitamin B6 status and growth of neonates at birth.

To evaluate the adequacy of maternal pyridoxine supplementation during pregnancy for both maternal and neonatal status at birth, vitamin B6 status, assessed by plasma pyridoxal phosphate (PLP), pyridoxal (PL) and total aldehyde vitamer (PLP + PL) concentrations, and the growth of neonates, including weight, length, head and chest circumferences, were examined for 209 neonates whose mothers were supplemented with 0, 1, 2 or 3 mg pyridoxine.HCl (PN.HCl)/d during pregnancy. Maternal PN.HCl supplementations were positively correlated to both maternal (r = 0.62) and cord (r = 0.78) plasma PLP concentrations (p < 0.0001). Mothers supplemented with 2 or 3 mg/d PN.HCl had significantly higher plasma concentrations of PLP and total B6 aldehyde vitamer in maternal and cord blood compared with those receiving 0 or 1 mg PN.HCl/d. A growth benefit for neonates whose mothers had maternal and cord plasma PLP concentrations > or = 40 nM was revealed by the maternal supplementation of 2 mg PN.HCl/d during pregnancy. Thus, in healthy pregnant women, according to our study, a daily supplement of 2 mg PN.HCl provides the adequacy of maternal and neonatal vitamin B6 status and the satisfactory growth of neonates at birth.

Intrauterine elimination of pyridoxal 5’-phosphate in full-term and preterm infants

This study addressed the intrauterine elimination of pyridoxal 5'-phosphate (PLP) in 15 preterm and 31 full-term infants, thereby providing estimates of fetal vitamin consumption as well as maternal vitamin requirements during pregnancy. Elimination was calculated as the difference in the plasma PLP concentration between umbilical vein and umbilical artery times the umbilical plasma flow. Plasma flow in the umbilical vein was calculated from pulsed Doppler ultrasonographic determination of blood flow and from the hematocrit value. Plasma PLP concentrations were assayed in maternal and umbilical veins and the umbilical artery; PLP concentrations were similar in preterm and full-term infants (P > 0.05). In both groups of infants the PLP concentration in the umbilical vein (preterm: 100.3 nmol/L; full-term: 63.9 nmol/L) was ninefold higher than in maternal circulation (P < 0.001). In full-term infants, PLP concentrations in maternal and umbilical veins correlated weakly (r = 0.358, P < 0.05), but no significant correlation was found in the preterm group (P > 0.05). The arteriovenous concentration gradient of PLP in cord vessels was higher in preterm infants (15.0 nmol/L) than in full-term infants (2.1 nmol/L), but the difference between groups was not significant (P > 0.05). Preterm infants eliminated 1.7 nmol PLP.kg-1.min-1 in utero, whereas full-term infants eliminated 0.2 nmol PLP.kg-1.min-1 (P < 0.05). The significantly higher plasma flow in preterm infants (116 mL.min-1.kg-1) compared with full-term infants (78 mL.min-1.kg-1) contributed to the higher PLP elimination in preterm infants.

Erythrocyte and plasma B-6 vitamer concentrations of long-term tobacco smokers, chewers, and nonusers

Erythrocyte and plasma B-6 vitamer concentrations were determined in males aged 25-55 y who were long-term smokers, chewers, or nonusers. Tobacco users had either smoked (n = 23) or chewed (n = 11) for > 15 y; nonusers (n = 11) had never smoked or chewed. All subjects had normal hematocrit values. Food energy, protein, and vitamin B-6 intakes of the three groups of subjects were not significantly different. All subjects had fasting plasma pyridoxal-5'-phosphate (PLP) concentrations indicative of adequacy. Erythrocyte B-6 vitamer and 4-pyridoxic acid (4-PA) concentrations of all three groups were not significantly different. Nonusers had significantly higher plasma PLP concentrations than did smokers, whereas PLP concentrations of chewers were intermediate between the two groups. Chewers had significantly higher concentrations of plasma pyridoxamine-5'-phosphate (PMP) than other groups. Plasma pyridoxal, pyridoxine, pyridoxamine, and 4-PA concentrations of the three groups were not significantly different. Differences in some B-6 vitamer concentrations in plasma but not in erythrocytes were observed between tobacco users and nonusers.

B-6 vitamer concentrations in mouse plasma, erythrocytes and tissues

The five major forms of vitamin B-6, pyridoxal 5'-phosphate (PLP), pyridoxal (PL), pyridoxamine (PM), pyridoxamine 5'-phosphate (PMP) and pyridoxine (PN) were measured in plasma, erythrocytes, liver and brain of A/Ibg and DBA/2Ibg mice by paired-ion High Pressure Liquid Chromatography. The mice were fed a non-purified diet that provided the bioavailable equivalent of approximately 3–4 mg PN-HCl/kg diet. In each tissue two of the vitamers accounted for nearly all of the total concentration of vitamin B-6. These were: plasma, PLP (14%) and PL (85%); erythrocytes, PLP (94%) and PL (3%); liver, PLP (63%) and PMP (36%); and brain PLP (55%) and PMP (43%). PM and PN contributed negligible amounts to the total vitamin B-6 content of these tissues. There were no significant differences in the concentrations of any of the vitamers between the two mouse strains, however, Pearson correlations between pairs of indices were different in the two strains. For example, plasma and liver PLP concentrations were uncorrelated in the A, but negatively correlated in the DBA mice. These data suggest that although plasma PLP may be a suitable index of dietary intake of vitamin B-6, genetic factors may be an important variable in the ability to predict tissue concentrations of the B-6 vitamers from plasma or erythrocyte concentrations.